There are several sections in this website that
you should read regarding track wiring. This section on track wiring,
Part I, covers general wiring information, testing, and troubleshooting.
Part II contains
the actual wiring of track. The menu to the right will automatically
take you to the right section.

If you want to buy your wire and connectors from your
favorite NCE dealer, NCE is selling
wiring kits in 25, 50, and 100 foot lengths. It can be used with any
DCC system. Check out their
100 foot kit. It's a .pdf file. You will need Adobe
Reader to read it.

SUGGESTION: Buy Several Boxes of Different Colored
Push Pins.

These are cheap, sanity saving devices. Use one color
to mark rail "A". Use another color to indicate that a section
of track has been wired. Use another to indicate a problem rail switch
to the track gang.

Use a 3156 or 1156 Automotive Taillight Bulb to
Limit Current to a Track Sub Bus.

The 1156 taillight bulb has been around for years,
but it is starting to get scarce. The new version of the 1156 is the
3156. The science is the same for both bulbs, so read what I have below.
Then I wrote about the 3156 and using it. Also,
before I get into taillight bulbs, I write about the increasingly popular
LED.

Can You Use an LED Instead of a Bulb?

Unfortunately not. A light bulb works because its resistance
increases when it heats up and lights. This increased resistance is
how a light bulb limits a short. The resistance of an LED does not increase
when it heats up. So it won't work.

If you are tempted to try it anyway, you will find that
the LED will not allow your locomotive to properly receive the DCC signal
and power. Your locomotive will not run properly. Furthermore, if you
have a short, your LED will burn out very quickly.

Should You Use Taillight Bulbs, Circuit Breakers, or
Neither???

The use of light bulbs to limit current has
been occurring long before I was born. Heck, even the use
of car taillight bulbs in model trains wasn't my idea. Since
the bulbs I saw in an old Model Railroader were all obsolete, I
ran tests and determined that the very low cost #1156 was the optimal
choice. Other than publishing my findings here in my web
page, I would have expected this to be the extent of my contribution
to the hobby on this topic. Instead, I've not only evidently
sold tons of bulbs — with not a bit of thanks from the bulb manufacturers!
— but the topic continues to generate a ton of email on the Internet. Since
the topic is still not clearly understood by all, I thought I'd
come back and rewrite things and try to do a better job by adding
a few things that have been learned over the past few years.

Why use taillight bulbs? A taillight bulb
is a low cost way to limit current when a short occurs on your
layout. Shorts typically occur when a train derails or when points
and wheel sets are out of tolerance and touch. When bulbs are
used to supply power to a sub bus, only that sub bus will be affected. The
train(s) in that sub bus will stop. Any other trains attached
to that same booster will not. As an extra bonus, the bright
light provides quick localization to a short — it lights up your
feet!

Why use bulbs? Why do they work regarding shorts? A
light bulb is cheap and seemingly simple. Why use them to limit current
in shorts? What makes them work?

A light bulb when it is off and cool has a very low
resistance. If this was all there was to a light bulb, it would be
useless in protecting shorts. However, its very low resistance allows
the train to receive nearly full voltage and current. So when there
is no short it is as if the bulb was nothing more than a piece of wire.

When a short occurs, a much higher amount of current
attempts to flow to your track. This much higher current causes the
light bulb to light. This is where the important thing happens. The
bulb is very hot when lit. The wire inside bulb has what is known as
a positive temperature coefficient. When the temperature goes
up so does the resistance of the bulb. The resistance of the bulb now
has a much higher resistance than when it was cold. This
higher resistance limits the current to the short.

When the short goes away, the current flowing through
the bulb drops off. The bulb cools. It goes back to having a very low
resistance and your train runs again.

It is not the intent of this website to talk
you out of buying circuit breakers. Since the
bulbs are much less expensive than electronic circuit breakers,
you can afford to have more of them. This allows you to
sub divide your layout into smaller electrical pieces in an effort
to more
quickly localize a short when one occurs. This is
why I and others use bulbs instead of circuit breakers. It's
a choice you have and thought you might like to know about it!

Make
sure the bulb doesn't touch anything. It gets hot when it comes
on. You don't want to risk fire. It is cold when the bulb
is not lit.

Why not use taillight bulbs? It is not a circuit breaker. It
is not a substitute for a circuit breaker. It limits current
to a short. It does not stop it altogether as a circuit breaker
would. If you want or need a circuit breaker, use a circuit
breaker. Both Tony's Train
Exchange and Digitrax sell
electronic circuit breakers for use with DCC.

Taillight bulbs do not make shorts go away. If
a short takes place, you will have to resolve it right then and there
— just as you would if you didn't use them. The same goes for circuit
breakers.

I must warn you, however. There will still be a lot
of current flowing through the short, as well as all the wires and
trackwork leading up to the short. Enough heat can be generated to
melt ties and do some minor welding. The group I am associated
with has wooden ties. We haven't had any side effects like welding
or melting, but I understand that it has happened to some people, so
I felt you should be fairly warned.

So you may want to put a switch in series with the bulb.
As soon as a short develops, you can hit the switch. I personally
don't bother with switches. If I'm worried about melting, burning,
or damaging anything I would hit the master kill on my DCC throttle. You
will rarely feel the need to do this.

Do you have to use taillight bulbs or circuit breakers? Positively,
absolutely, not. The use of either the bulb or the circuit breaker
is simply to subdivide a layout into smaller electrical pieces for
easier troubleshooting. Also, when a short triggers either of
these devices, only trains in that smaller electrical section are affected. Not
using either of these devices simply means a bigger portion of your
layout will shut down when a short takes place. This is hardly
a catastrophe.

So why did I ever bother looking into taillight bulbs? Before
command control of any kind, not just DCC, derailments took place,
but they only affected one train, one operator, and one power pack. No
one thought anything of it. This is how it had always been since
my first train set!

But when a club I was in went DCC, every short shut
down the entire layout. (The DCC system we were using at the
time compounded the problem by sending a shutdown command to all boosters,
whether that booster was truly affected or not.) Three or four
shorts an operating session per each of the fifteen or so operators
meant the entire layout was shutting down an average of every three
minutes. People were rapidly getting disgusted with DCC!

With ancient, inconsistent, undocumented, and in some
cases, incorrect wiring, as well as turnouts and things that weren't
in gauge any more, finding the source of the shutdown never had us
shutdown less than five minutes and usually more like fifteen. Without
electronic circuit breakers available at the time and the bank already
broken outfitting the large layout with DCC, I went after the age old
solution of taillight bulbs before a posse went and lynched the DCC
equipment manufacturer.

A few years later I joined a club that had just gone
with a non-DCC command control. History repeated itself. Now
a veteran of the taillight, I showed up the next week with a fist full
of fixes.

Should you use taillight bulbs or circuit breakers? This
is perhaps the most important question you need to answer for yourself. The
more boosters you can afford to have, resulting in a layout that is
broken up into smaller electrical sections (known as booster districts),
the less you will have a need for either bulbs or circuit breakers. The
fewer operators and trains you have, the less likely an aggravating
short will take place. The more perfect your trackwork, turnouts,
rolling stock, and locomotives are in, the less likely you will have
a short. Now if you could only keep momentarily inattentive operators
from trying to run through a turnout thrown against them!

The majority of shorts occur at turnouts. Avoid
minor welding, melting ties, and lighting that bulb, or tripping the
circuit breaker or booster; use DCC friendly turnouts if you can. The
use of DCC friendly turnouts, discussed in the turnout
section of this web page, is not required. It is simply another
choice you have as a modeler.

The clubs I have been in and their members have come
to love the bulbs. Members building layouts at home are building
the bulbs in from the start. They like the ease of troubleshooting
the bulbs provide and they really like the floor lighting up in the
vicinity of the problem.

The choice of either or neither is completely yours. This
web page simply wants you to know your choices.

Can you add them later? Yes. If you
think you might, then seriously consider putting in sub buses now. This
is especially true if you might use bulbs. If you don't, it will
definitely be much more difficult, but not impossible, to add breakers
or bulbs later.

How long your sub buses are, is not nearly as important
as installing them in the first place. You will have to add
sub buses in some way to use bulbs. You can always cut sub buses
in half. Especially if you want to use bulbs, where very short
sub buses are part of the attraction to using bulbs, look at the layout
wiring diagrams in this web page to understand the usage of sub buses.

Do taillight bulbs always work? No. Most
manufacturers of modern boosters will shut down before the taillight
will activate.

Fast Acting Boosters:The Digitrax Chief has
an option that delays the Chief's internal shutdown mechanism. The
EasyDCC booster has a component you can change to delay its internal
mechanism. I
will gladly list those boosters which bulbs can or cannot be used with
if you write
me with the information. Since long trains of lighted passenger
cars sometimes necessitate the use of a slower shutdown mechanism,
other boosters can probably accommodate the use of bulbs as well.

Lighted Passenger Trains:
Lash-Ups, MU'ing:
Sound in Locomotives:If you have long, lighted passenger trains, you might have trouble.
The bulb may come on partially all the time. Multiple-Unit lash-ups may
cause bulbs to come on. Lots of locomotives with sound have also been
reported to cause bulbs to come on partially all the time. That said,
I routinely run double-headed articulated trains with sound up a 3.2%
grade and
don't
have a
problem.

Boosters That Are Running Within About 2-3 Amps of
Their Rated Capacity:If you booster is anywhere near its rated capacity, your booster
may trip before the bulb warms up and starts limiting current. One way
you can avoid this problem is to buy higher capacity boosters or just
buy more boosters and run less trains on them. I'm not advocating that
you spend extra money on boosters. I'm only telling you that could do
this. What I am telling you is that if you do not routinely run your
boosters near their limits, bulbs will probably work for you. I allocated
my boosters based on what the maximum number of locomotives I might run
in a district. But since I don't typically run that many, bulbs work
fine for me.

Working On The Various Scales:Below I listed
the various scales and whether you can use bulbs or not. If too much current is drawn under normal operating
conditions, the bulb will light. This isn't what you want! In
all cases, if you can't use a bulb, you can use a circuit breaker if
you want to.

G scale: Do not use bulbs for G scale. You
probably don't have so many trains and operators that this would be
an issue for you anyway.

O and S: Bulbs will probably only work
with O and S scale locomotives with high quality motors.

HO: Of course! If you have double
headed trains, you shouldn't have trouble using bulbs. Triple
or more may light the bulb. High quality locos, low or no grade,
and more locos than cars :) may work fine.

N, Z: You can probably lash five locomotives
together. One word of caution when using bulbs for these smaller
scales. As noted earlier, bulbs do not cut stop the short, they
merely limit the amount of current below the trip threshold of the
boosters. But these currents are still fairly high for the small
components in these smaller scales. Melted or otherwise damaged
parts are entirely possible. The operating environments that
N and particular Z are used in may not even make bulbs an appealing
option to be considered.

Can you use taillights and circuit breakers? Probably
not. You probably wouldn't want to anyway. They both serve
the same goal — to limit the amount of a layout affected when a short
occurs.

Should you use sockets with these bulbs? The
cheapest socket I could find for these bulbs was $4. Tail light bulbs
are designed to go on and off a zillion times. If you used DCC friendly
turnouts and laid your track well, hopefully these bulbs will light
infrequently and last a lifetime. I received an email saying
someone installed them in the 50's on his layout and has yet to burn
one out.

One reason to use a socket is if you plan to use the
bulb as a switch - that is, if you plan to remove the bulb to isolate
a section of track. A switch and the socket are essentially the same
price so go for it. Since I use micro switches with Switchmaster
turnout machines and slide on lugs for the micro switch, I can just
slide the lug off the micro switch to act as a switch.

Make
sure the bulb doesn't touch anything. It gets hot. You
don't want to risk fire.

Even if you bought a socket, you would have trouble mounting it in a
panel — because the socket is made to go into a car, not a control
panel. Forget mounting it in a panel. Let it hang under
your layout. You won't have any trouble seeing it when it lights.
It's a 25+ watt bulb. It will light up your feet! Plus,
its lighting up coincides with a locomotive stopping. So whenever
a locomotive stops, everyone affected looks at the floor to see where
the problem is.

Reader Ed Collins makes his bulb mounts as follows: He
just took a standard #6 spade. Took a punch and opened up the slot on
the end you solder the wire in. Flattened it out, drilled a small hole
large enough to get the pin on the side of the 1156 bulb into it. Solder
the spade on the side of the bulb. Works fine and you do not have to
try and buy a special connector.

Digitrax Chief Owners: You will have to
set the Chief option #18 to 'closed.' This causes the DCS100 to
delay for 1/2 second before reacting to a short circuit, rather than
the 1/8 second it comes set to from the factory.

Are They Hard to Find? This bulb isn't as popular
in cars as it used to be. While you can still get them at auto supply
stores and discount stores automotive departments, you may want to try
D. Erwin's suggestion. He tells me http://www.sunraylighting.com will
sell in bulk and at wholesale.

3156 Taillight Bulb

The 3156 is the modern version of the 1156. As you can
see from the photo, the 3156 uses a plastic base instead of a metal
one. On the right side of the photo, you can see that the 3156 has a
wire termination. There is another wire on the other side.

You can bend these terminations and remove the plastic
base. You will need to pull firmly to remove the plastic base. Keep
pulling. It will come free. You can then slide the terminations under
the screw of a terminal strip. That's good because the metal blade (the
"3/4 W solder terminal series 140") that I used on the 1156's is
now obsolete and no longer available. And of course, you don't have
to spend any additonal money for mounting the 3156. You may need to
trim the leads a little bit before securing them to a terminal strip.

SUGGESTION: Attach Your Sub Bus Feeders With Screw
Terminals.

If you have a short that is troublesome to find, you
will be able to disconnect the feeders. Otherwise.... you will have
to start cutting your carefully soldered wires. I've seen this happen
more than once, I'm afraid. I prefer soldered connections, too. But
here, soldering will work against your troubleshooting efforts.

The following two drawing show how I like to anchor
the ends of the sub buses as well as attach to the main bus. The first
arrangement shows if you are using bulbs. It could be a DCC circuit
breaker. The second shows the use of a block detector and a bulb. These
are just ideas that you can use for seeds for your own desired arrangement.

Do note that this arrangement causes the block to be
fed from one end. If you are using heavy wire and short blocks, this
works well. For example, my blocks are no longer than 15 feet long
and I use #14 or #12 wire for sub buses. The 15 foot length is simply
so I can detect a train every 15 feet. You could probably double this
without any noticeable affect on your train operations.

It has the physical advantage of providing a place to
anchor the end of each block — no loose ends. Also, you precisely know
where one block ends and the next begins.

SUGGESTION: Develop A Color Code - And Stick To
It!

If you have to make a trip back to your favorite home
improvement store to get more wire, do it! Your sanity is at stake
here!

In fact, let me suggest a color code based on the fact
that many of you may want to use regular house wiring. White for the "common" bus
feed. Remember common bus feeds between booster districts are NOT to
be connected together! Black for your main bus. Clear or green for
your sub buses. See the schematics and read on for clarification.

If you use the bare copper wire as part of your feeder
system, be careful it doesn't contact anything that is grounded to
your home wiring. Worse, beware of contacting any other voltage
sources — such as the wires going to your booster power transformer
that perhaps you haven't gotten around to putting in a box.

SUGGESTION: Get Your Wire From Your Favorite Home
Improvement Store.

This has its advantages. Probably the most important
one is that if you run out, you can easily get more wire. This convenience
will help you stick to your color code scheme. Also, the price may
be more reasonable than any electronic supply store.

At a home improvement store you can find:

Heavy stranded wire. At Home Depot, they stock:

14 AWG: Blk Beige Red Blu Grn Wht

12 AWG: Blk Red(Rose) Wht Blu Org Yel Brn Grn

10 AWG: Brn Org Yel Blk Red Blu Wht

Heavy solid wire for wiring homes. This stuff
is cheap, so may want to base your power distribution
buses on this.

Light solid wire for wiring phones and thermostats.

Telephone wire is the thinnest solid wire available.
It only comes in 4 conductors. It could be used for your booster network
where you are running a separate heavy ground. Telephone wire is red,
black, yellow, and green.

Thermostat wire is solid and available in 4, 6, and
8 conductors. So you may want to use this for running LocoNet and particularly
the booster network. It is heavier than telephone wire, so it is less
likely to break. The 4 color wire is red, green, white, and yellow.

Antenna rotor (or rotator) wire is stranded. It is also
available from Radio Shack. It comes in 4, 5, and 8 conductors. It
is generally not color coded.

Heavy duty color coded antenna rotor wire is available
from amateur radio supply stores. Ask a ham radio operator where one
of these is or when the next hamfest is. If you don't know a
ham, don't worry about using this type of wire.

While there is a lot to be said for stranded wire, if
you use the brown ribbon antenna rotor variety, you may have a difficult
time figuring out which edge of the ribbon is the first wire under
a dimly lit layout.

By the way, your local home improvement store also has
an amazingly good selection of heat shrink tubing and tie wraps.

SUGGESTION: Good Track Connection Practices
Come First.

Make sure you lay your track and join rails together
in a manner that you think is the right way. I don't know that I really
should get into this since I haven't lived long enough to see all the
ways it could be done and how well they hold up.

Considerations:

Some people don't solder switches in place so they are
easy to remove if they need any work.

Some people don't like to solder too many pieces of
track together due to expansion considerations. You definitely need
to consider the temperature swing in your layout room. Is it in the
house or out in the garage?

So after deciding what your track laying practices are
going to be, follow this basic rule: Every piece of track should be
soldered to something. That can be another piece of track or a wire.
The wire can be a feeder or a jumper from the adjacent rail. DO NOT
count on a metal joiner to carry power to the next rail. It WILL let
you down eventually. I expect you knew that already.

SUGGESTION: Using Insulation Displacement
Connectors (IDC).

An article by Tony Koester in the August 1998 Model
Railroader discussed using insulation displacement connectors. These
are commonly used for installing aftermarket automotive products like
car alarms. Frequently they are used to clip onto existing wires for
power and ground. Not surprisingly, someone might want to use them
to connect to DCC power busses.

An insulation displacement connector is a type of connector
that has a fork with a knife edge. It can pierce a wire's insulation
and make good electrical contact with the encased wire. There is no
need to strip a wire and the connection can be made in a second.

This type of connection has been used by phone companies
for several decades. Their reliability, WHEN USED PROPERLY, has been
proven.

Using them properly, requires that you do these things:

1. You MUST use the proper one for the wire sizes you
will be using. If you are using one that is too small for your wire,
it
may bite into the wire too much. It might then break. If too large,
a poor or non-permanent connection may be made.

2. If you must unclamp the IDC, do not reclamp it exactly
where it was previously. When clamped, it must clamp onto a fresh location.
This location does not need to be far. The location of the bite need
only be a fresh one. An 1/8" or 2mm is adequate.

3. Use the tool 3M makes for squeezing the IDC around
the wire. Based on reader experience, this seems critical. Trying to
save a few dollars and using a pair of pliers results in IDCs that
fail.

Do NOT tug any wire or allow any strain to be imparted
onto a wire attached using an IDC. There is no way for me to say how
much is too much. At one extreme, you have the telephone application,
where the cabling is installed and virtually never touched. Works great.
At the other extreme, you have fragile computer ribbon cables that
are occasionally misapplied to save money in applications where the
cable may be moved several dozen or more times. They fail. Ribbon cables
inside computers generally do okay if the person is mindful of them.

It is almost inevitable in the life of a layout that
some tugging to troubleshoot a problem will be done. Or maybe you will
need to add or remove some track necessitating the need to tug on wires.
Or, in pulling new wires, they get slightly wrapped around existing
wires and some strain is imparted.

You may find yourself having to disconnect feeders should
you have to troubleshoot shorts. Do not reattach in exactly the same
place on the wires.

As long as you heed my cautions, using IDCs should work
well for you. With some strain inevitable, it is difficult to say if
you will start having problems several years from now.

These connectors are easy to install and may be ideal
for someone who hasn't developed the knack for soldering.

Soldering is still the best connection possible. If
you don't mind soldering, then stay with soldering. If nothing else,
soldering is cheaper.

One advantage of terminal blocks is that they force
a certain amount of neatness. They can be rigidly mounted in a fixed
location (you always know where it is) and it can be labeled. A splice,
IDC, solder, or any other type of "floating" connection (its location
may change whenever it is tugged) has minimal labeling (wrapped around
the wire) if labeled at all.

The photo of the IDCs in Model Railroader show the advantage
of a floating connection. It is close to where it is needed. It MIGHT
not need any labeling at all.

You can carry the floating connections too far. Even though
it seemed like a good idea at the time you did your installation, you
can easily end up with a unbelievable mess. You may have to do a lot
tugging to find out where wires go to or come from. If using IDCs,
lots of tugging is the last thing you want.

Use terminal strips where you would have used them
whether or not you used IDCs.

Label your wires. Any label at all that provides unique
identification of a wire is better than no label at all. Label the
wire frequently so you don't have to do a lot tugging. Labels at both
ends of a 20' long wire do you no good when you are in the middle!
Every other joist is good.

Avoid chaining. That is a IDC that is connected to a
wire that is connected to an IDC that is connected to a wire.....that
is connected to a bus. If you have a problem in this situation, it
could be difficult to troubleshoot. Hold yourself to two IDCs or less
between ANY track feed and a booster.

Also make sure your buses are continuous pieces of wire, mechanically
well connected at joints, like well twisted and soldered,
or use terminal strips. If using lugs on terminal strips, solder the
wire to the lug. In lugs, even if the wire doesn't pull out, tugging
on the connection could ultimately lead to a poor connection. Your
bus wires are your most important wires! Make sure the quality of their
connection to their sources (boosters) is without question! Make sure
it acts likes a continuous piece of wire and can withstand tugging.

Where to buy IDCs:

IDCs are common in car radio installation kits. But they
are not commonly used for home wiring or anything else. So you will
have a hard time finding them in any store of any kind. Modelers have
tried Radio Shack, auto stores, local electrical distributors and such.
Your best bet is a mail-order electrical components distributor like
Mouser. You will get the quantity you need at a good price as well
as a variety of choices - necessary to make sure you use the right
one
for
your
application. See the section on Getting Electronic
Parts for IDC part numbers and suppliers.

.

TESTING

RECOMMENDATION: Build a Short Detecting
Beeper BEFORE You Start
ANY DCC Track Wiring!

It's no accident that this recommendation is the first
in the track wiring section. If you wait until you find out you have
shorts, it's too late. Don't wait until you wish you had made one of
these. Do it now. It only takes a few minutes and a few dollars to
put together.

Of course, Radio Shack is gone. You can get a buzzer from
Jameco. Many buzzers will work.
I selected one from Jameco that
has leads and runs on a 9V battery. The Jameco
part number is 2117430. Their part number for a 9V battery clip is 1949488,
Then attach this instead of a booster to your track while doing
all wiring. Any wiring error that you make that results in a short will
cause an immediate beeeeeep. This is before you've soldered the
wire or hooked up twenty feeders only to find nothing works! Use this
thing religiously.

If you have several boosters, you will need to move the beeper to
each booster district as you wire. Alternately, if you have a team
wiring several districts at once, temporarily jumper the main booster
feeders together so only one beeper is needed.

You could also mount the circuit in a bobber caboose
or clip it to the track with alligator clips. Be sure the boosters
are not connected to the track. I cannot emphasize this
enough. The booster will appear as a short to the beeper. Nothing
but the beeper should be attached to the track. This includes things
like Frog Juicers and auto reversing controllers. These are great products,
but you will need to install them last because they will all cause the
buzzer to sound.

You can use a light bulb instead of a buzzer. Light bulbs
are a less sensitive than the buzzer. But if you use a light bulb, be
constantly looking at it. You can easily be wiring happily
along and not notice the light.

Also note, do not use an LED if you are using Frog Juicers
and electronic auto reversing controllers. Like the buzzer, and LEDs
are very sensitive. If you do use LEDs, hook up the Frog Juicer and
electronic auto reversing controllers last.

You can use an ohmmeter, but you will get squirelly results. So don't
do this unless you have a very good understanding of exactly
how an ohmmeter works.

For a club, you might want the following buzzer:

It is designed to have the buzzer attached to the track
whenever the DCC is not on. This is so people don't forget to use the
buzzer. C1 is 25V or higher 1000uF capacitor. R1 ohms = (Vbooster -
Vrelay)/Irelay. R1 wattage = (Vbooster - Vrelay) x Irelay. R1 may not
be needed at all as some relays will run fine at 14V without damage.

A Simple Test Indicator Light for DCC

Contributed by Don Vollrath

Many times during construction or troubleshooting there
will be a need to verify if there is DCC voltage between the proper
track rails as expected …or not… or if the polarity is reversed
across gaps in the track, or if anything on the other side of the gap
is even connected. One may be tempted to use a voltmeter or an LED type
tester to help perform the task. However these instruments can sometimes
be too sensitive and yield confusing results, particularly where long
wire or track rails are involved. The simple reason is the continuous
polarity switching of DCC voltage can cause a minute amount of ‘leakage’
current to flow even when something is seemingly unconnected. This can
cause a sensitive LED to glow or an AC voltmeter to read something unexpected.

A more positive solution is to use a small incandescent
bulb that draws significant amount of current for such testing. When
an incandescent bulb needing more than 10 milli-amps (ma) is used there
is no doubt that DCC voltage is or is not present between the two probed
points. Either the bulb lights up or it doesn’t.

You can make your own probe using a 14V, 30ma bulb such
as Miniatronics #18-014-10. A convenient ready made probe type tester
with a clip on lead found in automotive parts stores under the BALKAMP
brand draws about 200 ma on DCC power.

First, let's discuss how we should refer to the voltage
we measure. This is more for those already familiar with AC voltage
measurements. If you are not, skip to the next paragraph so that
you can measure your DCC track voltage and current.

AC is usually measured with qualifiers such as "rms", "average", "peak",
and "peak-to-peak." DCC is square wave AC. What should
we call it? Extreme few of us own "true-reading rms" meters,
so forget rms. Only old analog meters, with a needle, read average. Peak
and peak-to-peak refer to a ground reference. A decoder has no
way of knowing any such reference. So do either of these have
meaning to us? While technically, all these can be used
to refer to DCC voltage, the only thing that really matters is what
the absolute peak voltage applied across the input leads of a decoder. Many
devices can be used with DCC. These often contain documentation
that says "do not exceed 24 volts" or something to that effect.

So what I do is convert DCC to DC, to be measured by
a standard DC voltmeter, and simply refer to it as volts. Technically, "peak" would
be the applicable term. Use the circuit below to convert DCC
to DC and follow the directions below.

Function

Value

Radio Shack P/N

Peak Reading

Z1
C1
R1

1N914
0.1uF, 50 WVDC
--- omit ---

276-1122
272-0135
---

Average Reading

Z1
C1
R1

1N4001
4.7uF, 50 WVDC
10k, 1/4 W

276-1101
272-998
271-1335

This circuit assumes that you are using a digital
volt meter with an input impedance of at least 1 mega ohm.

Radio Shack P/N

Alligator Clips

270-356

Banana Plugs

274-721

Should you build the average or peak reading circuit?
Don Vollrath has the following suggestions for you.

The Average voltage detector should be used to measure
and adjust the 'normal' DCC track voltage level. Use this for general
track voltage measurements, anywhere on the layout, with and without
track loads. Always useful to detect track voltage drops due to poor
connections or poor DCC bus wiring.

The Peak detector is useful to help visualize how much voltage ringing
is on the system, w/o having to use a multi-K-buck oscilloscope. If
the peak V is >2X the average V, one should be adding R/C suppression
networks to help prevent problems.

This circuit will convert DCC square wave AC to standard
DC. However, before you get excited and measuring DCC track voltage,
you need to calibrate this circuit. Here's how.
1. Take your meter and set it to read DC volts. Measure the DC
voltage across a 9V battery.
2. Now set your meter to read DC voltages. Hook to the circuit
above. Instead of DCC track, hook the input of this circuit to the 9V
battery.
3. The difference between the readings is an offset due to Z1 above. You
will need to add this number to every DCC track voltage reading you make. If
you made the above circuit on a little circuit board, write this number on
the circuit. Don't forget, you will need to add this offset every time
for the most exact reading possible!

This circuit is a very slight variation on the above. It
allows you to measure the amperage drawn by your DCC equipment. You
could use the above circuit with the capacitor if you want to. Without
the capacitor, you will get a more exact reading.

SUGGESTION: How to Know If Your Wiring is
Adequate — The "Quarter Test"

All manufacturers will tell you, your wiring MUST pass
this test: If you short your track at any point with a coin or
tool, it MUST cause your booster to shutdown. If it does
not do so consistently and everywhere on your layout you try, including
powered frogs, your wiring is inadequate. Melted plastic
is likely and a fire is definitely possible. Your steam trains
and diesels with shot rings are the only things that should be smoking
on your layout — not your benchwork and wiring!
If you are using light bulbs as I suggest on this website, the light should light brightly. A half lit or dim bulb is a sign of inadequate wiring.

In order for this test to work, your booster
must have an adequate power supply. Your booster must be
supplied by a power supply that has a current rating equal to or
greater than the booster's rating. If not, this test will not work.
You may falsely think your booster is not working properly or your
wiring is inadequate when the problem is really your power supply
is too small. Do not use your old DC power pack to power your booster.
It probably cannot put out enough power to operate your booster properly.
See the section on booster network wiring.

If shorting your bus trips your booster but shorting your track does not, you have inadequate feeders. For those who know a little bit about electricity, you may be confused by measuring the bus voltage at the feeder under the layout and reading the same thing as you measure on your track. You might be led to think they everything is good. There is a little bit more about electricity that you need to know. Voltage only drops when you have a load. If you measure the track voltage with a load - such as an operating locomotive or a car tail light bulb - you will then see the voltage drop at your track. This is a little science fair project. Once you do it, you will learn that measuring the track voltage is not a good way of testing if your wiring is adequate. In summary, let me repeat, if shorting your bus at the bus/feeder connection trips your booster but shorting your track does not, you have inadequate feeders; bad connections to your track, bus, or both; or all of the above.

If you are using IDCs (insulation displacement connectors), you must be using the ones intended for the wire size you are using, they must be installed using the proper tools, and you cannot reuse them.

If you soldered your wires, did you get a good solder joint? It should have a nice, smooth finish, no brown residue, and no blob.

Did you solder your wires to the track and/or bus? No? That's your problem. Solder wires to your track. If not using IDCs on your buses, solder your feeders to your bus.

Are you using 24 AWG wire for your feeders? They must
be short and frequent. You must pass the quarter test or your wiring
is inadequate.

SUGGESTION: Use a Volt Meter to Check
Your Track Polarity with the Beeper.

If you always use the beeper and are sure you hook it
up the same way, a volt meter can help you verify that your "A" rail
is really the "A" rail. Just hook up your beeper and then measure the
voltage it produces with your voltmeter.

SUGGESTION: DCC Track
Power Polarity Identification

DCC track power is a form of AC. But it helps you keep things straight
while you wire if you keep thinking of it the same way as you did with
DC. You still have two wires and you need to know which is which. This
is especially important topside. With your layout winding every which
way, it's easy to lose track.

Call them "+" and "-", "A" and "B", "Tarzan" and "Jane",
whatever you like. Avoid "inside" and "outside" rail because unless
you have a simple oval, chances are your inside rail will become your
outside rail at some point.

Track Polarity Car

Here's a great visual aid if you have trouble keeping
track of which rail and wire is which or if you are troubleshooting
a wiring problem. You only may need one car if you are wiring your layout.
If you are troubleshooting a wiring problem, two may be useful.

Paint the car any colors you want. You may find it to
be a good idea to paint the car the same colors as your bus wires. You
probably see where this is going. Five-finger the car around your layout
and check your bus wires, if already installed, or install your bus
wires as you go.

Any type of car will work as well as a cheap car that
normally won't stay on the track.

TROUBLESHOOTING: Don't Waste Your Time Trying
to Find a Short With an Ohm Meter.

It never works. I really wish it did! The
typical ohm meter, digital ohm meter, etc. just isn't sensitive enough.
Save you energy for doing it in a way that is guaranteed to get
results. That is....tip # 5-21.

TROUBLESHOOTING: Train Does Not Operate Properly When Crossing
Between Booster Districts.

Below is a simple way to determine if all is well with your booster wiring when a locomotive goes from one booster district to the next. All you need is a 14V-16V (for HO) light bulb. Two boosters are shown
below.

Note that the boosters are connected together with a ground wire.
Either connect this to the ground connection on your booster, if there is one, or to the booster case if there is not. This ground wire should not be connected to the ground wire that connects to your home's wall socket (earth ground).

Your boosters receive their DCC signal from a network cable that connects between all the boosters and command station. Some manufacturers have a booster built into their command station.

One of the boosters can be in reversing mode. Both boosters should NEVER be in reversing mode at the same time. If they are, stop now, and make only one booster at most a reversing booster. Likewise, if you are using reversing units, the same thing applies.

Follow my directions below. Don't skip steps as each step will help you identify a particular problem.

Step 1 Step 2

Step 1: A light bulb connected between the rails connected to booster A should light. If not, stop. One or both of the wires leading from your booster to the track is not connected to the booster.

Step 2: A light bulb connected between the rails connected to booster B should light. If not, stop. You could have the same problem as in step 1.

Step 3 Step 4

Step 3: A light bulb connected between the red rail of booster A and the blue rail of booster B should light. If not, you may not
have a good ground between the boosters or you do not have good phasing between boosters. To check phasing, swap the wires going to your track from ONE (1) of the boosters and try this step again.

Step 4: A light bulb connected between the blue rail of booster A and the red rail of booster B should light. If not, you may not have a good ground between the boosters. If step 3 passes, passing this step should just be a confirmation that all is well.

Step 5 Step 6

Step 5: A light connected between the red rail of booster A and the red rail of booster B should NOT light.
If it does, even glows a little, then either your boosters do not have a good ground between them or the boosters are putting out different voltages. If you need to measure your track's voltage, see the section above on measuring DCC.
If your bulb is excessively bright or burns out in a flash, then you probably have a common rail problem. See the section on common rails in the Track Part 2 page of this website.
If you have converted an existing DC layout to DCC, this is likely your problem.

Step 6: A light connected between the blue rail of booster A and the blue rail of booster B should NOT light. If it does, even glows a little, then you may have the same problems as described in step 5.

If you are still having problems, are you using boosters from differing manufacturers? They may not play well together.

If you train changes speed as it crosses between booster districts, you may have the boosters set to different output voltages. Consult your booster's manual for instructions on how to properly set the output voltage of your boosters. In some cases, this may be as simple as flipping a switch on the front of your booster.

TROUBLESHOOTING: A Short Between Rails of Track.

How can you have a short on a block of track that has
no turnouts or crossings? This sounds far-fetched, but I have seen it
twice this past year. The soldered feeders from a bus to BOTH rails
shorting everything out. While this sounds like the person was really
stupid, it really isn't that hard to do. How many times have you checked
the rail on the top is the one you are about to connect a wire to. All
you have to do is do this one enough times.

TROUBLESHOOTING: Divide and Conquer Bus
Feeder Problems.

Okay, you've spent several hours trying to find a short with an ohm
meter. You've given up and now you are going to cut feeders. Start
with the first feeder and go down the line. Right? What
if you have 16 feeders on a bus and the problem is feeder #14? You
have already resolved yourself that this will be the case thanks to
Murphy's Law. So you begin at feeder one and start cutting. No! Try
something called a binary search instead. Here's how it
goes. Follow the example, please, and then we'll get to some
practical considerations.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Problem

Put your ohm meter or handy beeper in place of the booster. Break
the bus in the middle - between feeder #8 and #9. You cut the
bus in half. This is the "binary" part of this thing. The
short then goes away. Now the "search" begins! Since you
have disconnected the meter from #9 thru #16, you know the problem
is not with #1 thru #8. So reattach your meter to the bus at
#9. Your meter reads a short again.

9

10

11

12

13

14

15

16

Problem

Divide the bus in the middle again; this time between #12 and # 13. #13
thru #16 are now disconnected and the short goes away. You know
the problem is not with #9 thru #12. Reattach the meter at #13. The
short is back.

13

14

15

16

Problem

Divide between #14 and #15.

13

14

Problem

This time the problem stays. It's either #13 or #14. Cut
feeder #13. The short is still present. The problem is
#14.

So how many cuts did you have to make? Four. If you had
started at #1, it would have been fourteen! Imagine the number
of cuts saved if you have more than sixteen feeders!!!

Notice if you had 32, or even 64, it would only have been 1 or 2
more cuts respectively. Beats 62 cuts, doesn't it? You
can zero in on the problem feeder in just five minutes! Now think
about how little time it will take to repair the bus compared with
reconnecting 62 feeders!

Now as practical matter, you just hacked up your bus in three places. So
perhaps you just do the first two cuts above or whenever you get down
to about four feeders. You will definitely need to do a good
soldering job in repairing your bus.

Moral, and to avoid hacking up your bus any more than necessary:

Use a beeper from the very beginning. (See the first
tip in this track wiring section.)

Consider using screw terminals so you are not cutting
feeders frequently.

Use light bulbs, breakers, or even toggle switches and separate
your buses into sub-buses that don't have so many feeders.

If you have not used DCC friendly rail switches, consider
power routing them through a light bulb or a toggle switch. Note: Since
rail switches are the "Achille's heel"* of model railroading. If
you are not using DCC friendly turnouts, you should seriously consider
bulbs or toggles. If a short develops and it is the fault of
a rail switch, you can rapidly go down the line flipping toggles
off until the short clears. (If you prefer toggle switches,
you will find that bulbs are much cheaper than toggle switches. Sorry
about that.)

One of the beauties of DCC is that except for rail switches, gaps
in the track that you didn't put anything in, and any wires underneath
that you didn't insulate that might touch, you aren't likely to have
wiring problems.

*I don't mean to offend any rail switch manufacturers.
It's the nature of the beast, not the quality of your construction.
The same applies to real railroads!

SPECIAL
SITUATIONS

INFORMATION: Wiring Australian "Accept" Yard Signals

I was
recently asked: "I had a yard on my standard DC powered layout
with "Accept" signals. This controls entrance of trains into
a yard. With a simple circuit, trains could leave when the light
was red, but trains could not enter. Is there an easy way to
do this with DCC?"

I suspect the simple circuit was a relay and a diode. Darn
simple! Sorry, nothing that simple can be done in DCC
or any command control system. I suggest you put a block on either
side of the signal. The block behind the signal would have current
sensing. This could trigger a Digitrax DS-54 turnout controller
or possibly a Wangrow SM-104. The DS-54, and I believe the SM-104
as well, has outputs that can be on for a number of seconds. (The
DS-54 can do 12 seconds.) So a departing train could leave using
the turnout controller to activate a relay that would energize the
block in front of the signal. In the case of the DS-54, the throttle
could turn on the block in front of the signal and turn the light green. Again,
I feel fairly certain the SM-104 can do this, too.

Some decoders, like the Digitrax decoders, can keep their
functions active in the presence of DC. So instead of killing
the block in front of the signal completely, use a relay to apply DC.
An approaching train, with the appropriate CV set to stop when
no DCC signal is present, will stop. The decoders also have a
CV that allows the functions, like the headlights, to remain on if DC
is present. Some people call this a "break generator."